1. Technical Field
The present disclosure relates generally to radio frequency (RF) devices, and more particularly, to ultra-high coupling factor monolithic transformers for integrated differential RF amplifiers in system-on-chip (SoC) devices.
2. Related Art
Generally, wireless communications involve a radio frequency (RF) carrier signal that is variously modulated to represent data, and the modulation, transmission, receipt, and demodulation of the signal conform to a set of standards for coordination of the same. Many different mobile communication technologies or air interfaces exist, including GSM (Global System for Mobile Communications), EDGE (Enhanced Data rates for GSM Evolution), and UMTS (Universal Mobile Telecommunications System) W-CDMA (Wideband Code Division Multiple Access). More recently, 4G (fourth generation) technologies such as LTE (Long Term Evolution), which is based on the earlier GSM and UMTS standards, are being deployed. Besides these mobile communications modalities, local area data networking modalities such as Wireless LAN (WLAN)/WiFi, WiMax, and so forth.
A fundamental component of any wireless communications system is the transceiver, that is, the combined transmitter and receiver circuitry. The transceiver encodes the data to a baseband signal and modulates it with an RF carrier signal. Upon receipt, the transceiver down-converts the RF signal, demodulates the baseband signal, and decodes the data represented by the baseband signal. An antenna connected to the transmitter converts the electrical signals to electromagnetic waves, and an antenna connected to the receiver converts the electromagnetic waves back to electrical signals.
Depending on the particulars of the communications modality, single or multiple antennas may be utilized. The output of the transmitter is connected a power amplifier, which amplifies the RF signals prior to transmission via the antenna. The receiver is connected the output of a low noise amplifier, the input of which is connected to the antenna and receives inbound RF signals. Thus, the power amplifier and the low noise amplifier, along with the antenna switch that selectively connects the antennas to a respective one of the output of the power amplifier or the input of the low noise amplifier, serves as key building blocks in RF transceiver circuitry. These components may be referred to as a front end circuit.
Conventionally, in order to lower manufacturing costs and allow full integration of a complete RF System-on-Chip (SoC), a complimentary MOSFET (metal oxide semiconductor field effect transistor) technology is utilized for the power amplifier and the antenna switch circuitry. SoC devices with integrated front end circuits intended for mobile communications applications require both a high sensitivity receiver, a power amplifier with a low error vector magnitude (EVM) floor, and a local oscillator, all on a single semiconductor die. Local oscillator pulling and substrate noise coupling render differential amplifiers a robust choice, and small form factor integrated circuits suitable for mobile applications are possible with differential circuits that incorporate coupled inductors.
One challenge associated with differential power amplifiers and low noise amplifiers is in the design of baluns for differential to single-ended signal lines and regular transformers for differential to differential signal lines, with high coupling factors in a standard CMOS (complementary metal oxide semiconductor) process. Currently, an edge coupled transformer is utilized, where the typical coupling factor is approximately 0.7 or lower. A further challenge relates to the increases in insertion loss of the balun and the transformer at the input of the low noise amplifier or the output of the power amplifier. As the number of inductive coils in the printed circuit structures increases for the high levels of coupling that are needed, there is understood to be a commensurate increase in insertion loss. This may result in an increased noise figure of the low noise amplifier, along with a decreased linear output power of the power amplifier. As a consequence, increased current consumption may follow, as well as decreased gain for the low noise amplifier and/or the power amplifier chain.
Accordingly, there is a need in the art for improved geometries and winding structures of the printed balun and transformer that meet the foregoing challenges.